Typically, furniture cushions are commonly made in one of two types: foam core or spring core. Foam core cushions are the most common. They typically consist of a polyurethane foam core, fabricated by cutting from a larger slab or bun, and typically have a layer of polyester fiber applied to the top and bottom, or wrapped “bull-nose” top, front and bottom. Spring cushions are less common, typically preferred by higher end furniture manufacturers. They typically consist of a pocketed spring core, surrounded by a top and bottom layer of polyurethane foam, and a four-piece boxing made of polyurethane foam. The bottom layer is assembled with the boxing pieces using adhesive, the coil unit inserted into the cavity created, and the top foam layer glued in place to enclose the coil unit. The resulting assembly is then typically covered as above with a layer of polyester fiber.
There are other types of cushion constructions, usually designed for specialty markets. One such construction is the all-fiber cushion used in the outdoor furniture market. This construction contains only one type of material, although the layers of polyester fiber may be of various densities.
Foam cushions have their advantages. A foam core is very easy to fabricate—the desired thickness is slit from a bun, and the width and depth are cut from the slab. Odd shapes or sizes are easily cut from the slab or bun stock.
Foam cushions also have their disadvantages. Foam is relatively expensive; foam cost has been rising significantly faster in recent history than most other types of raw materials. The cost of foam is more volatile in general than other types of cushion components. Foam scrap from the fabricating process is not fully recyclable—it can only be shredded for use in low-value products or for making re-bonded foam. Foam loses a significant portion of its support very early in its life cycle, so a foam core cushion will lose support characteristics quickly during its life cycle, and will continue to lose support over the entire life cycle, leading to decreased consumer satisfaction and increased consumer returns. Foam has significantly less push back when a load is removed, compared to the resistance of the foam when the load is applied—this is felt by the occupant as less push from a cushion when getting up from the seated position. Foam is difficult to manufacture with consistency, and any given lot of foam will vary in its density and firmness. Foam is the most flammable of the cushion component choices. Smoldering foam creates toxic and explosive gases. Burning foam creates toxic gases. Foam cannot be manufactured with any post-consumer recycled content. Used foam is not practical to recycle.
Traditional spring cushions have their advantages. A coil spring unit (pocketed coil or otherwise) retains most of its support characteristics throughout its life cycle, so a cushion made with coils will retain more of its original support throughout use. A coil spring unit is more resilient than foam, pushing back with essentially the same force when a load is removed, as it resists the load when it is applied. Coils are typically much more consistent in firmness than foam, so any cushion made with coil content will typically be more consistent than a foam cushion.
Traditional spring cushions also have their disadvantages. Fabrication costs are higher, as the typical traditional spring cushion as described above will require six pieces of foam to be cut and sub-assembled, then assembled with the spring core. The foam component remaining in the top and bottom layers of the traditional spring cushion still share the same disadvantages as listed in the foam cushion above, although those disadvantages are proportionally less bothersome as the percentage of foam content decreases due to the use of a coil unit.
Fiber cushions have their advantages. Fiber will not retain water like foam, making it appropriate for use in outdoor cushions. Flammability is reduced compared to foam cushions, as are toxic or explosive by-products of burning. Fiber is more easily recyclable than foam.
Fiber cushions also have their disadvantages. Lofted fiber will lose height over its life cycle, which is seen as loose cushion covers and felt as a loss of overall seat height.
Finally, to make an acceptable finished cushion, the user must be insulated from the feel of the individual coils.
It is therefore an objective of this invention to reduce, or preferably eliminate, polyurethane foam from upholstered furniture cushion construction.
Another objective of this invention has been to provide a method of making a furniture cushion that reduces the labor and overhead associated with traditional methods of coil cushion construction.
Yet another objective of this invention has been to accomplish the previous objectives without compromising the ability to insulate the user from the feel of the individual coils.